The daughter Elizabeth appears in 1871, aged 10 b Pimlico (which was part of the missing area in 1861). Charlotte (12 in 1871), Caroline (7 in 1871) and John (5) were also born in Pimlico, so it looks like it was their home for the relevant stretch of time.
The family’s address at the time of Elizabeth’s birth, which is the one closest to the 1861 census date, should appear on her birth certificate.
Elizabeth Downs, mother’s maiden name Page, Jun qtr 1861 St George Hanover Square 1a 270.